The present invention relates to a recording apparatus for linewise recording information upon a moving photoreceptor.
Apparatus for recording information upon a moving photoreceptor are known comprising a multiplicity of stationary pointlike radiation sources that are distributed along a recording head extending transversely of the direction of displacement of a photoreceptor, and that are individually energizable for information-wise exposing the photoreceptor in response to received information signals as the photoreceptor moves past the recording head.
The transfer of the images of the radiation sources onto the photoreceptor can be achieved by means of lens arrangements, fiber optics or fiber pipes, self focussing fibers, or the like.
It is usual for the recording head to comprise two parallel staggered rows of the radiation sources. In comparison with the use of a single row of radiation sources the spacing between adjacent sources of a row can in those circumstances be doubled while achieving the same image resolution.
It is considered in the art that at least 10 irradiated points per mm are required on the photoreceptor, so that for recording an information line across a standard DIN A4 photoreceptor, which has a width of 216 mm, a recording head comprising at least about 2200 discrete radiation sources is required. A plurality of light sources in the form of LED's (light-emitting diodes) can be formed as an array on a monolithic semi-conductor chip. By line-wise assembling a plurality of chips, a recording head having a length of 216 mm can be obtained.
When using radiation sources disposed in two rows, the illumination of the sources forming the more downstream row, reckoning in the direction of motion of the photoreceptor must be delayed relative to the illumination of the sources of the other row in order that the projected images of the different rows of sources shall be on a common transverse line across the photoreceptor.
Apparatus wherein such a delay occurs are disclosed e.g. in GB Appl. 2,042,746 A of Savin Corporation, relating to a multiple variable light source photographic printer, and in European Appl. 82 201 324.9 of Agfa-Gevaert N.V., relating to a recording apparatus.
In order to obtain very satisfactory results from the mentioned delay technique above referred to, it is necessary for the speed of advance of the photoreceptor to be kept rigorously constant. In the absence of a constant speed, the points irradiated by the different rows of light sources will not coincide on the same line of the photoreceptor, so that after development a "stepped" line form is obtained. The mentioned image defect is usually small, and is acceptable in recording apparatus for the production of office copies and the like. The defect is, however, not acceptable in recording apparatus for the production of high quality line prints, e.g. prints produced in digital medical diagnostic systems.
It is possible to provide to synchronise the operation of the electronic recording means with drive mechanism for the photoreceptor, by electronically coupling the drive to the synchronization impulses of the recording signal. But this requires a complicated driving system which may notably affect the cost-price of the apparatus.